Threaded plastic plug for forced screwing

ABSTRACT

A threaded plastic plug ( 1 ) comprises a single-piece structure, having a longitudinal axis ( 2 ) of symmetry, and comprises a head ( 5 ), a body ( 3 ) with an outer thread ( 6 ) and a cylindrical collar ( 17 b), and a tightening flange ( 4 ) interposed between the head ( 5 ) and the body ( 3 ). The head ( 5 ) has the shape of a tubular solid ( 8 ) projecting from the flange ( 4 ) in a direction parallel with the axis ( 2 ) of the plug ( 1 ), and comprises an inner cavity ( 7 ), accessible from the outside through one end of the solid ( 8 ), the cavity ( 7 ) being laterally surrounded by a non-circular surface ( 22 ) of an annular wall ( 9 ). The wall ( 9 ) of the tubular solid ( 8 ) which surrounds the cavity ( 7 ) having a variable thickness, the greater thickness being located close to the flange ( 4 ) and entirely facing towards the inside of the cavity ( 7 ). [FIG.  1]

This invention relates to a threaded plastic plug for forced andfacilitated screwing.

In the prior art there are already threaded plugs, made of plasticmaterial, intended for industrial use, designed to be inserted withforced screwing and tightening in a hole of a generic recipient unit.Such plugs are used for the most diverse purposes, including, forexample, blocking holes, protecting them from any damage, covering themfor functional or aesthetic reasons, making them airtight or watertight,marking them, hermetically sealing them, etc.

A prior art type of such plugs has an overall single-piece structure,having a longitudinal axis of symmetry. It basically has threeidentifiable fundamental parts: a body, a flange and a head, parts whichare positioned one after another longitudinally relative to the axis ofsymmetry.

The plug body is substantially cylindrical, hollow inside, and has aprofile wall in which an outer thread is made, this thread beingdesigned to couple with a matching thread made in the hole which willreceive the plug.

The flange is basically ring-shaped, and is interposed between the bodyand the head. It projects transversally to the axis of the plug relativeto both the body and the head. When the plug is used the flange isdesigned to make contact with a section of the surface of the unitsurrounding the hole, applying a thrust action on it as a result ofscrewing, the thrust action being more intense the higher the tighteningtorque used for forced screwing of the plug into the hole.

The head has the shape of a tubular solid with a prismatic profile,extending over a short axial length, projecting from the opposite sideof the flange to that from which the body projects.

The tubular solid has a large inner cavity which, laterally, issurrounded by a thick wall, having the shape of a closed ring and witheven, constant thickness. The inner cavity also has a closed end, formedby the flange. A large opening located at the top of the tubular solidallows access from outside to the inner cavity of the plug head.

In the prior art plugs described above the head has various types ofcoupling surfaces on which to engage an operating tool for forcedscrewing or unscrewing of the plug.

Of said coupling surfaces: first coupling surfaces are on the faces ofthe outer surface of the ring-shaped wall of the tubular solid; secondcoupling surfaces are in contrast provided by prominent protrusionscontained in the cavity.

More particularly, the first outer surfaces are substantially at rightangles to the plane in which the flange lies and are shaped and sized insuch a way that they can be coupled with an operating tool consistingfor example of a standardised, standard-production open-ended wrench ora socket wrench normally used for tightening steel bolts.

The operating tools indicated above—irrespective of their technologicalproduction form—always operate by encompassing from the outside theouter surface of the tubular body of the head and couple with thatsurface with some circumferential play which is always present andcannot be eliminated.

The second coupling surfaces, which are in contrast provided by theparallel protrusions inside the cavity, instead together delimit aninterposed slot or slit in which a further type of operating tool may beengaged, again of the standardised type for generic usage, in that caserepresented by a screwdriver which can engage in the slot so as to applythe force necessary for screwing/unscrewing the plug.

As already indicated, the plug is normally made of plastic material. Theoperating tools of the standard type are in contrast made ofhigh-strength steel and are sized in such a way that they can applytightening torques whose intensity is suitable for tightening steelbolts fully home. Consequently, due to the high capacity for force whichcan be generated using these tools, when they are used forfitting/removing plastic plugs, the intensity of the tightening torquemust be very carefully modulated so as to always guarantee the correctcompromise between plug tightening suitable for the specific functionsrequired of it, and tightening which is not excessive and which is belowa limit value which could cause permanent damage to the plug head;damage which is also contributed to by the non-eliminablecircumferential play with which the operating tool engages with thefirst and/or with the second coupling surfaces previously defined.

In practice, when fitting the plugs it may be the case that in order tostay relatively safe regarding the possibility of damaging the plug, thefitter may tend to tighten the plug in a cautious way, less than isnecessary to guarantee for example optimum hole airtight or watertightsealing.

That may result in subsequent problems which could lead to damage notjust to the mechanical unit which receives the plug, but also,indirectly, to the machine or plant to which that unit is operativelylinked.

On the other hand, over-tightening of the plug may cause other, no lessserious, problems. In fact, although it is true that a high level oftightening, for example enough to permanently deform the head of theplug, could indirectly provide assurances about the efficiency of theairtight or watertight seal of the plug, it is equally true that ifduring the operating life of the plug in use it becomes necessary toremove the plug (for example for routine or extraordinary maintenance ofthe unit or of the parts of the machine which use said unit) anypermanent deformation of the plug could even prevent application of theoperating wrench, preventing the consequent correct unscrewing andremoval. Paradoxically all of that may make routine maintenance workvery laborious and expensive, sometimes with the aggravatingcircumstance that added to such difficulties operating the plug therecould be further difficulties operating the tools due to the location ofthe plug—relative to the unit and/or the plant which uses the plug.

Another significant problem presented by the use of operating toolssuitable for tightening steel bolts, relates to the fact that, again dueto their capacity for developing intense tightening torques, whenscrewing in the plug, if the plug thread has not been correctly engagedin the receiving hole thread, it is quite easy to cause permanent damageto the plastic thread of the plug. If that happens, it could result indefects in the hermetic seal, with potential continual dripping ofliquids, with the risk of compromising the reliability of the unit whichuses the plug.

Therefore, when fitting the plugs, it is important to pay properattention to the initial screwing step, finding the start of the threadand correctly engaging it in the receiving hole.

In the prior art said operation can be carried out in a relatively shortunit time, which however, when multiplied by a large number of productsto be assembled in mass-production, is no longer negligible. However,that aspect may also be worsened by the possible, not infrequent lowtechnical skill and sensitivity of the labourers assigned theseoperations, meaning that a fitting operation which is relatively simple,when not carried out correctly, can actually become critical for thereliability of the machine which receives the plug.

The main aim of the invention is to overcome said disadvantages byproviding a plug shaped in such a way that it can receive a tighteningtorque which may even be very intense, without being subject topermanent deformations which would compromise the functionality of theplug or vice versa the correct nature of any subsequent plug removaloperations which might be necessary.

In accordance with that aim, the head of the plug is shaped in such away that it has walls surrounding the head cavity which have a thicknessthat is increased at least close to the flange, as well as being locatedcompletely inside the head cavity in such a way as to avoid anylimitation on the use of plug operating tools made in the standardisedform. Another aim of the invention is to allow the automatic and correctengagement of the body thread irrespective of the relative position withwhich the plug is presented to the receiving thread.

The technical features of this invention, in accordance with the aboveaims, are clear from the content of the claims herein, in particularclaim 1, and from any of the claims directly or indirectly dependent onclaim 1.

The advantages of this invention are more apparent in the detaileddescription which follows, with reference to the accompanying drawingswhich illustrate preferred, non-limiting embodiments of the invention,in which:

FIGS. 1, 2 and 3 are respectively an elevation view, a top plan view anda side view of a plug made according to the invention;

FIG. 4 is a perspective view showing the plug in its entirety;

FIG. 5 is a cross-section of the plug in the plane of the line labelledA-A in FIG. 2.

With reference to the accompanying drawings, in FIGS. 1, 2, 3 thenumeral 1 denotes in its entirety a threaded plug 1, intended to beinserted with forced screwing in a hole made in a generic receivingunit, not shown in the accompanying drawings. The plug 1—preferably madeof plastic material—basically comprises a single-piece structure, havinga longitudinal axis 2 of symmetry, and formed by: a body 3, a flange 4and a head 5, which are positioned in an orderly fashion one afteranother along the axis 2, with the flange 4 interposed between the body3 and the head 5. The body 3 [FIGS. 4 and 5] is hollow inside and, onthe outside, has a thread 6, which it is assumed will mate with amatching inner thread in the hole in the unit that will receive the plug1. The thread 6 is interposed between two smooth cylindrical collars 17a and 17 b, one 17 a of which is adjacent to the flange 4, while theother 17 b is made at one end of the body 3 far from the flange 4.

By comparing FIGS. 2, 4 and 5 it can be seen that the head 5 has theshape of a prismatic tubular solid 8, with a polygonal profile, which inthis particular case is hexagonal. The tubular solid 8 extendslongitudinally relative to the axis 2 of the plug 1 over a short length,projecting from the flange 4 on the opposite side of the flange to thatfrom which the body 3 projects.

The tubular solid 8 has an inner cavity 7 which, laterally, issurrounded by a thick wall 9, having the shape of a closed ring; andwhich is inferiorly delimited by a closed bottom surface 21, formed bythe flange 4. At the top of the tubular solid 8 there is an opening 11allowing access to the inner cavity 7 of the plug head 5.

More particularly, on the outside of the wall 9 of the tubular solid 8which surrounds the cavity 7 there is a lateral surface 9 e which issubstantially at a right angle to the plane in which the flange 4 lies,and on the inside of the wall there is an inner lateral surface 9 i,correspondingly polygonal, which is oblique relative to the axis 2 ofthe cavity 7, diverging from it in the direction of travel along theaxis 2 from the body 3 to the head 5 of the plug 1.

The thickness of the wall 9 is variable from a minimum located at theaccess opening 11 to the head 5 inner cavity 7, to a maximum which incontrast is located at the zone where the tubular solid 9 is attached tothe flange 4. The variation in the thickness is preferably continuousand linear and is fully obtained inside the cavity 7. In that way, thereis a noticeable increase in the strength of the wall 9 of the tubularsolid 8 without thereby causing any modification of its outer lateralsurface 9 e which may therefore be engaged correctly and without anylimitation using operating tools of the standardised and standard type.

Returning to the body 3, it can be seen how the presence of thecylindrical collar 17 b in the plug 1 means that for correct insertionand initial engagement of the thread 6 in the matching thread of thereceiving hole, the fitter does not need to search for the start of thethread. In practice it is sufficient to begin screwing the plug1—whatever its condition—in order to make the thread automaticallyengage correctly, without any action by the fitter, after rotating theplug 1 about its own axis 2 at most through half a round angle.

Therefore, all of that allows any damage to the plug to be avoided,helping to guarantee its perfect seal and correct tightening, and alsohelping to reduce both the initial fitting times and the working timesrequired for any subsequent maintenance, with obvious advantages interms of reducing the related costs of production and/or maintenance.

The invention described above is susceptible of industrial applicationand may be modified and adapted in several ways without therebydeparting from the scope of the inventive concept. Moreover, all detailsof the invention may be substituted by technically equivalent elements.

1) A threaded plastic plug (1) comprising a single-piece structurehaving a longitudinal axis (2) of symmetry, and comprising a head (5), abody (3) with an outer thread (6), and a tightening flange (4)interposed between the head (5) and the body (3); a structure in whichthe head (5) has the shape of a tubular solid (8) projecting from theflange (4) in a direction parallel with the axis (2) of the plug (1),and comprising an inner cavity (7), accessible from the outside throughone end of the solid (8), the cavity (7) being laterally surrounded by anon-circular surface (22) of an annular wall (9); the wall (9) of thetubular solid (8) which surrounds the cavity (7) having a variablethickness, the greater thickness being located close to the flange (4),the plug (1) being characterised in that the body (3) comprises a smoothcylindrical collar (17 b) preceding the start of the outer thread (6) ofthe body (3) and designed to allow automatic engagement of the threadirrespective of the relative position with which the plug (1) ispresented to the receiving thread.